1. Field of the Invention
The present invention relates to an X-ray imaging apparatus which takes an image of an object such as the jaw and facial area, tooth area and otolaryngologic area of a human body, along a desired tomographic plane.
2. Description of the Related Art
In the field of medical X-ray diagnosis, there is well known an X-ray CT (computed tomography) apparatus which takes a CT image of an arbitrary site of a human body. In such an X-ray CT apparatus, an X-ray source and X-ray imaging means opposed to the X-ray source are revolved by 360.degree. around an object of an arbitrary site such as the head or trunk to obtain image information, which is processed by a computer to obtain a CT image which is a section view of the arbitrary site. Such an X-ray CT apparatus of the prior art is bulky and expensive, and hence inadequate for use in the areas of dentistry and otolaryngology.
In dental treatment, if the thickness and structure of the jaw are known prior to an implant operation or the like, the operation can be easily performed. In order to obtain such data, a miniature X-ray CT apparatus capable of obtaining X-ray CT images of a specific tooth and a vicinity thereof has been contemplated. Such a miniature X-ray CT apparatus comprises: an X-ray source for generating X-rays; X-ray imaging means for detecting X-rays which passed through an object; supporting means for supporting the X-ray source and X-ray imaging means so that they are opposed to each other across the object; and a driving source for moving the supporting means in a predetermined direction. When an X-ray CT imaging process is to be performed, the supporting means is revolved by 360.degree. around the object by the function of the driving source. During the 360.degree. revolution, X-rays which are emitted from the X-ray source and pass through the object enter the imaging means, and X-ray imaging is performed at predetermined angles. In such an X-ray CT apparatus, image information obtained in X-ray imaging at predetermined angles is stored in storing means, and the stored image information is subjected to CT image processing by a computer, thereby obtaining a desired CT image.
In an X-ray CT apparatus, images obtained as results of X-ray imaging at predetermined angles are subjected to the CT image processing. In the CT image processing, when an obstacle such as a metal prosthesis or a large bone structure exists in even one of the images obtained by the X-ray imaging, a clear CT image is hardly obtained by the computer processing because such obstacle absorbs a large amount of X-rays. In the case where an X-ray CT apparatus is used in the field of dental treatment, for example, a 360.degree. imaging process is conducted on the head of the human body. In a specific range of the imaging process, X-rays from an X-ray source pass through the vertebrae cervicales and then reach X-ray imaging means, and in the other range of the imaging process, X-rays from the X-ray source reach the X-ray imaging means without passing through the vertebrae cervicales. Usually the vertebrae cervicales easily absorbs X-rays. In the specific range a smaller amount of X-rays reach the X-ray imaging means because X-rays emitted from the X-ray source pass through the vertebrae cervicales, and hence a resulting X-ray image is relatively dark. To the contrary, in the other range of the imaging process X-rays emitted from the X-ray source do not pass through the vertebrae cervicales, so that a larger amount of X-rays reach the X-ray imaging means. Therefore, a resulting X-ray image is relatively bright.
Accordingly, when an X-ray CT apparatus is used in the field of dental treatment, the density of a resulting X-ray image changes depending on the angle of imaging at which the process of imaging the object is performed. When the degree of the change is considerably large, a satisfactory CT image can not be obtained in the subsequent CT image processing using a computer.
Such a problem exists not only in an X-ray CT apparatus, but also in a panoramic X-ray imaging apparatus which takes an image of the dental arch, and a linear X-ray imaging apparatus which takes only an image of a specific tomographic plane.